1+2+3+.+(n-1)化简

[3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 化简n分之n-1+n分之n-2+n分之n-3+.+n分之1 化简n分之n-1+n分之n-2+n分之n-3+.+n分之1 化简(n+1)(n+2)(n+3) 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 化简：1/(n+1)(n+2)+1/(n+2)(n+3)+1/(n+3)(n+4) 1/3[n（n+1）（n+2）]化简 化简3n(3n+1)(3n+2) -2n-(3n-1)化简 当n为正偶数,求证n/(n-1)+n(n-2)/(n-1)(n-3)+...+n(n-2).2/(n-1)(n-3)...1=n 化简[n^2+(n+1)^2]/n(n+1) 化简额 lim2^n +3^n/2^n+1+3^n+1 3(n-1)(n+3)-2(n-5)(n-2) n(n+1)(n+2)(n+3)+1 因式分解 n(n+1)(n+2)(n+3)+1等于多少 lim(n+3)(4-n)/(n-1)(3-2n) lim(n^3+n)/(n^4-3n^2+1)